For more information

Websites:

River Input Program
http://www-va.usgs.gov/chesbay/RIMP

Ecosystem Program
http://chesapeake.usgs.gov/chesbay

Simple Environmental Equation: Less Nitrogen = Healthier Chesapeake Bay

Fish and crabs in Chesapeake Bay have a chance to live in a healthier environment as a result of efforts to reduce the amount of nutrients entering the bay from its tributary rivers.

Pollution in the form of nutrients, such as nitrogen and phosphorus, enters the bay's estuary from its rivers and threatens the bay's health and productivity. Algal blooms, nourished by large amounts of nitrogen and phosphorus, block sunlight needed by grasses and other submerged aquatic vegetation, which are prime habitat for commercially valuable fish and crabs. The blooms also deplete oxygen from the water, depriving fish and crabs of much needed oxygen, resulting in fish kills.

Additionally, high nutrients are believed to be linked to the outbreaks of pfiesteria in the bay. A one-celled microorganism, Pfiesteria piscicida, was identified as a culprit in the 1997 Chesapeake Bay area fish kills, prompting Maryland officials to issue health warnings and to temporarily close rivers to commercial fishing and recreational activities. The fish kills in Maryland rivers seem to be associated with a combination of high nutrient concentrations, warm water temperatures, high salinity, and storm events.

In the early 1980's, Federal, State, and local governments began reducing the amount of nutrients in the rivers that flow into Chesapeake Bay. Bans on phosphorus detergent, upgrades of sewage-treatment facilities, control of runoff from city streets and farmland, and preservation of forest and wetlands were all designed to reduce the impact of nutrients on the bay.

USGS hydrologists and colleagues at several State agencies began the River Input Program in the mid 1980's to quantify the improvements in water quality resulting from those nutrient-reduction efforts. Partners in the River Input Program are Maryland, Virginia, and the Metropolitan Washington Council of Governments, under the auspices of the U.S. Environmental Protection Agency's Chesapeake Bay Restoration Program.

Crabs from Chesapeake Bay.

High flows of tributary rivers carry large amounts of nutrients and suspended sediment to Chesapeake Bay. USGS samples conditions like these at Conowingo Dam on the Susquehanna River.

After more than a decade of monitoring the amount of nutrients entering the bay, there is mixed news to report.

The good news is that Federal, State, and local nutrient-reduction programs are reducing the concentrations of nutrients in the rivers that flow into Chesapeake Bay. Where once researchers saw increasing trends in the concentrations of nutrients entering the bay from tributary rivers, they now see a leveling off or significant decreases. Phosphorus concentrations are declining in all but two monitored rivers. The decrease in phosphorus can be particularly attributed to effective environmental policy action by the States. The phosphate detergent bans enacted in Maryland, Virginia, Pennsylvania, and the District of Columbia during the mid 1980's lowered phosphorus inputs. Nitrogen, which is more difficult to control because of its many sources, is declining in all but four monitored rivers.

The bad news is that even though concentrations of nutrients have decreased, large floods in the last 5 years have increased loadings of nutrients into the bay. Researchers are just beginning to realize the impacts of those increased loads on the bay's living resources.

The return on the investment of scientific cooperation and proactive environmental policy is significant: the Chesapeake Bay is showing hopeful signs of restored health and habitat. Continuous monitoring has proven to be worthwhile in determining reductions in nutrient concentrations that have occurred as a result of human impacts. Further measures are needed, however, to deal with the forces of nature and to understand the effects of those forces on Chesapeake Bay.